Question: Charles can type $675$ words in $9$ minutes. How many words can Charles type in $13$ minutes?
Answer: We're trying to find the number of words Charles can type in $13$ minutes. If in ${9}$ minutes, Charles can type ${675}$ words, then in $1$ minute, he can type $75$ words.  So, in ${13}$ minutes, Charles can type ${975}$ words.